1. Field of the Invention
The invention relates to a device for separating a synchronous signal in a signal and a method thereof, and more particularly to a device for separating a synchronous signal in a video signal and a method thereof.
2. Description of the Related Art
FIG. 1 (Prior Art) shows a waveform of a video signal. Referring to FIG. 1, the video signal includes a synchronous signal SYNC and a data signal Data. The data signal Data and the synchronous signal SYNC has different level ranges. Usually, the voltage value that may be possessed by the data signal Data is greater than the voltage value of the synchronous signal SYNC. A receiver for receiving the video signal must first separate the synchronous signal SYNC from the video signal and then further generates a pixel clock according to the frequency of the synchronous signal SYNC and processes the video signal.
When the video signal is being transmitted, a DC level of an output of a transmitter is frequently different from a DC level received by the receiver. Consequently, the video signal received by the receiver may exceed a voltage range within which the receiver may operate normally. Thus, AC coupling is first performed according to the received video signal in order to separate the DC voltage from the video signal in the conventional synchronous video separating device. Next, a video clamping circuit is utilized to clamp the DC voltage level of the coupled video signal to the required voltage value. Then, a synchronous video separating device separates the synchronous signal SYNC in the video signal using a comparator according to a reference voltage because the synchronous signal SYNC and the data signal Data of the video signal have different level ranges.
However, an analog circuit is adopted to fix the AC-coupled video signal in the conventional video clamping circuit. The requirement of the analog circuit on the precision of the parameter is high, so the phenomena of the DC level fluctuation and the circuit bandwidth drift tend to occur under the interference of the factor of the IC manufacturing processes. The bandwidth of the circuit restricts the frequency range that can be processed by the synchronous signal SYNC. In addition, the utilization of the analog circuit tends to cause the problem of the unstable circuit, thereby increasing the complexity in design. Thus, it is a subject of the invention to solve the problem of the unstable circuit by effectively enlarging the frequency range of the video signal, which may be processed by the synchronous video separating device.